The invention relates to a steering gear comprising an electric motor, a control unit and a sensor system and to an electric power steering system equipped therewith. The invention relates in particular to a steering gear that is designed as a helical gear mechanism or a worm gear mechanism for an electric power steering system.
A steering gear of the type in question in the form of a helical gear mechanism for use in an electric power steering system is known from DE 19814719 A1. FIG. 1 shows the known steering gear 10, which comprises a housing, in which a helical gear, namely the worm wheel 40, and a helical pinion engaging therein, namely the worm 30, are disposed. The steering gear is equipped with an electric motor (stator 94, rotor 92), which is connected to the shaft of the worm 30 so as to drive the same. As is briefly described there (column 2, lines 48-49), the electric motor is controlled in the known manner by rotational speed and rotational direction sensors. It can therefore be assumed that an open-loop or closed-loop control unit and a sensor system, which can be disposed in or on the housing cover 12 of the electric motor for example, are also provided for controlling the electric motor there.
It is customary to provide the control electronics, and the sensors in particular, directly on, or at least very close to, the electric motor so as to exactly detect the rotational movement of the rotor. So as to actuate the electric motor, the rotational angle, the revolutions or rotational speed, and/or the rotational direction of the rotor must be determined as exactly as possible and be continually monitored. The customary arrangement of a sensor system directly on, or at least very close to, the electric motor is described in the following published prior art, for example: DE 10 2008 042 213 A1, DE 10 2008 040 318 A1 or DE 100 37 485 A1, wherein the latter reference refers explicitly to a steering gear in the form of a helical gear mechanism.
The sensors used are typically Hall sensors and/or magnetoresistive sensors (MR sensors), as is described in DE 10 2007 011 672 A1 or DE 102 21 340 A1, for example.
As far as the arrangement of the control unit is concerned, it is customary to likewise dispose the some directly on the electric motor, or at least very close thereto. For this purpose reference is made to DE 10 2008 001 503 A1 (see FIG. 1 or FIG. 2), for example, which comprises a control unit 9 that is disposed on the electric motor 8. While this published prior art refers to steering gears for a steering column drive, arrangements are shown of different embodiments with arrangements of the control unit (see FIG. 6) that are also typical of other steering gears. The control unit can thus be disposed laterally from the electric motor (see FIGS. 1 to 4) or axially offset at the rear end of the electric motor (see FIGS. 5 to 9). Because the arrangement of the sensor system is not explicitly described there, it can be assumed that the sensor system is integrated in the control unit.
Thus, steering gears are known in principle, comprising a helical pinion (for example including a worm), which are mounted in the gear housing and driven by an electric motor, wherein a control unit and a sensor system connected thereto are also disposed in or on the steering gear so as to detect and control the rotor position and/or rotation of the rotor of the electric motor.
The arrangement of the control unit and of the sensor system greatly influences the overall size (length and/or width) of the steering gear, which can make installation more difficult and increase the overall installed size. This must be considered in particular in connection with steering gears that are designed as helical gear mechanisms or worm gear mechanisms. One of the reasons is that the worm is typically mounted at the two shaft ends thereof and connected by way of one of the shaft ends thereof to the rotor shaft of the electric motor. This results in quite a significant, and often times hindering, length in the axial direction, which in many cases makes the steering gear difficult, or even impossible, to install.
Thus, it is the object of the invention to considerably improve a steering gear of the type mentioned above and the pivot bearing arrangement of the helical pinion shaft or worm shaft. This is intended to overcome the aforementioned drawbacks of the conventional solutions in an advantageous manner. In particular, savings of components are to be achieved and a compact design is to be proposed.